The present invention relates generally to turbofan aircraft gas turbine engines, and, more specifically, to exhaust nozzles therefor.
Turbofan gas turbine engines have various configurations for powering in flight aircraft of various sizes. The engines may be mounted to the wing, to the fuselage, or to the tail of the aircraft, and in these various configurations have nacelles which provide an aerodynamically smooth outer surface for the engines for minimizing aerodynamic drag during flight.
In a typical turbofan engine, an upstream fan is powered by a core engine extending downstream therefrom. The core engine includes in serial flow communication a multistage compressor, annular combustor, high pressure turbine, and low pressure turbine. The high pressure turbine powers the compressor through a suitable shaft, and the low pressure turbine powers the fan through another shaft.
The core engine is typically surrounded by a core cowling and is spaced radially inwardly from a surrounding fan nacelle for defining an annular fan or bypass duct. In operation, the core engine powers the fan to produce propulsion thrust by discharging pressurized fan air from a fan exhaust nozzle at the aft end of the fan duct. Some of the fan air enters the core engine and is compressed and mixed with fuel for generating hot combustion gases which are discharged through a corresponding core exhaust nozzle at the aft end of the core engine.
The fan nacelle may either be a short duct, with the fan nozzle being disposed upstream from the core nozzle. Or, the fan nacelle may be long and extend for the full length of the core engine through which both the fan air and core gases are discharged through a common exhaust nozzle.
The turbofan engine is designed for maximizing its efficiency of operation, and when mounted in an aircraft, the aerodynamic cooperation therewith must be addressed. For example, the engine nacelle must be suitably smooth and configured for minimizing aerodynamic drag in propelling the aircraft in flight. And, the engine should be configured for minimizing noise generated therefrom during aircraft propulsion, particularly during takeoff operation.
A significant component of aircraft engine noise is due to the high velocity of the core exhaust flow being discharged from the core nozzle. And, another noise component is due to the relatively high velocity fan exhaust flow discharged from the fan nozzle. As the aircraft is propelled in flight, the freestream ambient air has a relatively low relative velocity to the engine being propelled therethrough. The fan exhaust has a higher velocity and engages the lower velocity freestream air with a shear interface layer therebetween. And, the core exhaust has a higher velocity which engages the fan exhaust in shear in another interface layer therebetween.
Accordingly, a significant component of aircraft engine noise is attributable to the shear interfaces between the fan exhaust and ambient air flow, and between the core exhaust and the fan exhaust.
The prior art includes many patents in which exhaust nozzles are specifically modified for reducing noise generation during aircraft flight. Many of these configurations are complex and include various forms of exhaust tubes or lobes. And, lobed daisy exhaust mixers may also be used inside the long duct engines for mixing fan bypass air with core gases for reducing noise during operation.
However, these various noise attenuation components add weight and complexity, and also affect aerodynamic performance and efficiency of the engine, and therefore require a corresponding balance or compromise in the designs thereof.
Accordingly, it is desired to provide an improved exhaust nozzle for a turbofan aircraft gas turbine engine for attenuating noise while maintaining aerodynamic performance and efficiency.
A turbofan engine exhaust nozzle includes cooperating outer and inner mixers. The outer mixer includes alternating outer lobes and outer chutes. The inner mixer includes alternating inner lobes and inner chutes. Forward ends of the outer and inner mixers are spaced radially apart, and aft ends of the mixers are joined together to define an outlet of the nozzle for discharging exhaust flow.